The oxidation of Co(II) at a boron-doped diamond (BDD) electrode was investigated by use of anodic voltammetry. The results shows that this reaction takes place by a mechanism similar to that of cobalt metal oxidation in alkaline media. The voltammetric curves evidence a strong enhancement of the oxygen evolution current in the presence of Co(II). This behavior is consistent with cobalt oxide formation at the diamond electrode surface. Based upon these results, a simple, straightforward method for the production of high activity films on BDD electrode surfaces is demonstrated. The study of the electrochemical behavior in 1 M NaOH shows that the electrodes thus obtained exhibit promising, stable electrocatalytic performance for oxygen evolution, comparing well with those of thermally deposited cobalt electrodes. The use of BDD as a substrate for the electrocatalytic layers allows the deposition of isolated particles or discontinuous films, thus maximizing the utilization of the catalyst by avoiding the need for thick films. (C) 2003 The Electrochemical Society.